1. Field of the Invention
The present invention relates to a test socket capable of continuously and stably measuring the electric characteristics of an electronic device or semiconductor package, as well as to a method of forming contact terminals, i.e. contacts or contact pins for measurement purposes, of the test socket.
2. Background Art
There will be described a method of establishing electrical contact between contact terminals (contacts) of a conventional test socket (a socket provided for measurement purpose) and external connection terminals of an integrated circuit (IC) or a semiconductor package, by reference to an example of a surface-mounted IC, e.g., a quad flat package (QFP).
FIG. 10 is a perspective view showing an IC 10 to be measured and a test socket 60 having a plurality of contact terminals (contacts) 20. Contact terminals 20 of the test socket 60 are embedded in a housing 30 formed from an insulating member. External connection terminals 50 of the IC 10 are brought into pressing contact with contact planes 21 of the respective contact terminals 20.
FIGS. 11A and 11B are enlarged cross-sectional views showing contact between one of the external connection terminals 50 and the contact plane 21 of the corresponding contact terminal 20. FIG. 11A is an enlarged view showing the contact plane 21 of the contact terminal 20 and a contact plane 51 of the external connection terminal 50, and
FIG. 11B shows contact when the contact plane 51 is brought into pressing contact with the contact plane 21.
An oxide insulation film 52 (hereinafter referred to as an xe2x80x9coxide film,xe2x80x9d as needed) is present on the surface of the external connection terminal 50 of the IC 10 and possesses high electrical resistance. In order to ensure superior electrical contact, the contact surface 51 to be electrically connected must be brought into contact with the contact plane 21 by means of fracturing the oxide film 52. The external connection terminals 50 are further pressed to a certain degree while remaining in contact with the respective contact terminals 20, thus deflecting the contact terminals 20. As a result, relative slippage arises between the contact plane 21 of the contact terminal 20 and the contact plane 51 of the external connection terminal 50, thus removing the oxide film 52 and bringing the contact plane 51 into electrical contact with the contact plane 21.
Contact established by the foregoing conventional contact terminals (or contacts) suffers the following problem.
In association with fracture of the oxide film 52 of the external connection terminal 50, which results from relative slippage between the contact plane 21 of the contact terminal 20 and the contact plane 51 of the external connection terminal 50, a member 54 constituting the external connection terminal 50 (solder plating in this case) coagulates onto the contact surface 21 of the contact terminal 20. Greater relative slippage contributes to fracture of the oxide film 52 and enlargement of the contact area, thus effectively establishing superior electrical contact. However, the greater relative slippage also results in an increase in the amount of solder coagulating onto the contact plane 21. In most cases, the substance to coagulate corresponds to metal which oxidizes, such as solder. Through repetition of oxidation of the surface of the contact plane and deposition of the substance on the surface of the contact plane, contact resistance is increased, thereby preventing good electrical contact. More specifically, although relatively new contact terminals 20 establish good electrical contact, contact resistance is gradually increased with the number of times the contact terminals 20 are brought into contact with the contact planes of the external contact terminals 50 for measurement, thus rendering electrical contact difficult to achieve and shortening the life of the contact terminal 20.
Secondly, if superior electrical contact is not achieved, a non-defective IC may be determined to be defective, and the non-defective IC may be discarded.
Thirdly, if the percentage of ICs determined to be defective through erroneous determination exceeds a certain specified percentage, the group of ICs determined to be defective through erroneous determination is again subjected to determination, thus unnecessarily consuming time or incurring unnecessary costs.
Fourthly, the external connection terminals of the most current ICs tend to be arranged at narrower pitches. In association with this tendency, a contact failure is caused when foreign matter generated by an IC; for example, resin burrs or glass fillers contained in resin, is present between the contact terminal and the external connection terminal.
Japanese Patent Application Laid-Open No. Sho-58-199545 describes a measure for avoiding such a contact failure; i.e., a contact terminal whose tip end is formed into a plurality of sharp projections so as to establish contact by avoiding generation of foreign matter. However, since the projections of the contact terminal are sharp, the projections damage the external terminals, thus causing appearance or packaging failures.
The present invention has been conceived to solve the drawbacks of the conventional test socket, and the object of the present invention is to ensure stable contact between the external terminals of an electronic device and contact terminals of a test socket, thus realizing stable, continuous contact.
According to one aspect of the present invention, a test socket comprises contact terminals which are brought into electrical contact with external connection terminals of an electronic device or a semiconductor package, and each of the contact terminal has a plurality of protuberances and a plurality of recesses. The plurality of protuberances are formed from smooth curved surfaces in the portion of the contact terminals which contacts the corresponding external connection terminal, and the plurality of recesses are formed from smooth, curved surfaces adjacent to the respective protuberances.
According to another aspect of the present invention, a test socket comprises a plurality of contact terminals, and each of the contact terminals includes one or more contact projections provided on the surface thereof for contacting the external connection terminals of the electronic device or semiconductor package. The tip end of each of the contact projections being formed to assume a substantially spherical surface having a radius of curvature of 0.03 to 0.3 mm. Further, each of the contact projections has a plurality of minute protuberances and a plurality of minute recesses provided on the substantially spherical surface thereof formed from smooth curved surfaces.
According to still another aspect of the present invention, in a method of forming contact terminals of the test socket as stated above, the portion of each contact terminal, which contacts an external connection terminal of the electronic device or the semiconductor package, is machined to a desired surface roughness through electric-discharge machining. Then, the thus-roughened portion is plated with electrolytic nickel. Further, the thus nickel plated portion is plated with gold.
Other and further objects, features and advantages of the invention will appear more fully from the following description.